Method of preventing flashbacks in gas burner systems



g- 1954 H. H. ROBINSON, JR

METHOD OF PREVENTING FLASHBACKS IN GAS BURNER SYSTEMS Filed March 3,1949 FIG. I

FIG. 3

INVENTOR HARRY H. ROBINSON JR.

BY Z f 4 42 .M

ATTO R N EYI Patented Aug. 10, 1954 UNITED STATES PATENT QFFICE METHODOF PREVENTING FLASHBACKS IN GAS BURNER SYSTEMS Harry 'H. Robinson, Jr.,Staten Island, N. Y., as-

signor to xiii-Reduction Company, Incorporated, a corporation of NewYork Application March'3, 1949, Scriai'No. 79,442

5 Claims. 7 (Cl..158-118) This invention relates to gas burners,especially those of the oxyacetylene type, and particularlyto a methodand apparatus for preventing or minimizing the occurrence of flashbacksin gas burners.

One of the problems that has always confronted the gas burner artgenerally, and the oxyacetylene cutting, Welding and flame-treating artin particulanis'the prevention of back fires and flashbacks. The termsbackfire and flashback are frequently used synonymously, but it isintended that herein there be maintained a definite distinction betweenthem. A backfire is the rapid recession of the flame from the dischargeface cf the burner upstream into the burner, usually back to the mixerwhile a flashback is a continued burning of the gases within the burnerfollowing a backfire Backfires are generally caused by some temporaryreduction in gas flow, and while they'are'a'nuisance and undesirable,they are not usually serious. However, flashbacks may be very damaging,and unless immediately extinguished, may result in the necessity ofmaking costly and time-consuming repairs.

The principal object of this invention is to provide a new method ofpreventing or minimizing the occurrence of flashbacks in oxyacetyleneand other gas burners.

A further objeect is to provide apparatus by which the new method may becarried out.

The invention is based on the discovery that the injection of a smallamount of water, or other suitable vaporizable liquid'into at least oneof the gases supplied toa burner prior .to the formation of acombustible mixture of the gases will effectively prevent or at leastminimize the occurrence of flashbacks.

According to the invention, in a gas burner system in which twogasessuch as oxygen and acetylene are fed separately to a mixer whichsupplies the combustible mixture of the gases to the tip of the torch orother burner, a small amount of a vaporizable liquid, such as water, isinjected continuously during the operation of the burner into one orboth of the gasstreams either upstream of the'mixer or after the gasesenter the mixer but before they'have had an opportunity to mix. In anoxyacetylene burner system it is suiflcient to inject the vaporizableliquid into only one of the gas streams, and the particular stream intowhich it is injected is preferably the it will be in this phase when itis present in the gas mixture at the time of a backfire as hereinafterdescribed. It should be suspended in the gas in finely divided form andtherefore it is preferably in atomized condition when it is introducedinto the gas or placed in atomized conition by the flowing gas streaminto which it is introduced.

While I do not Wish to be confined to any particular theory as to whythe presence of the vaporizable liquid in the gas mixture prevents aflashback after a backfire, it is thought to be as follows: When abackfire occurs, all of the mixed gases in the system burn withexplosive rapidity and in so doing expand and are forced upstream of themixer. After the pressure wave caused by the explosive burning of themixed gases subsides, the fresh gases start flowing again toward themixer, and after they mix they are ordinarily re-ignited by thelingering hot active products'of combustion and continue to burn at themixing region, thereby producing a flashback. Presumably the water, orother vaporizable liquid, that is injected into at least one of the gasstreams and is present in the form of small droplets, vaporizesandabsorbs suflicient energy from the lingering active products ofcombustion of the backfire to deactivate these gases and thereby preventthem from re-igniting the mixture of the fresh gases. in the gas mixturein droplet or atomized form it presents a large surface area to promoterapid vaporization. Inasmuch as the principal function of thevaporizable liquid is to absorb heat, one advantage of utilizing wateras the vaporizable liquid is that it has a high latent heat ofvaporization, and therefore a small amount of Water'present in thecombustible gas mixture will absorb a large quantity of heat from anyactive products of combustion that may be present in changing from itsliquid phase to its vapor phase. Moreover, water is readily available inlarge quantities at low cost. For these reasons the preferredvaporizable liquid for introduction into one or both of the gas streamsis water, but any other vaporizable liquid, preferably a noncombustibleone, may be employed which will serve the purpose of cooling theproducts of combustion sufficiently to prevent them from reigniting thefresh mixture of gases.

Various types of apparatus may be employed for injecting the vaporizableliquid at the proper place into the gas supply of a burner system, twoof which are shown in the accompanying drawing, in which:

Figure'l is adiagrammatic representation of Since the liquid issuspended an oxyacetylene gas burner system having means for injectinginto one of the gas supply lines a liquid of the kind contemplated bythe invention;

Fig. 2 is an enlarged detail View in vertical section of the liquidinjector forming part of the burner system illustrated in Fig. l; and

Fig. 3 is a detail view in vertical section of another type of liquidinjector that may be employed.

Referring first to Fig. 1, a multi-flame gas burner represented insimple form at [9 is supplied with a combustible gas mixture from amixer H. Two gases, such as oxygen and acetylene, are fed to the mixerseparately from storage cylinders l2 and [3 through supply lines it and15. The water or other vaporizable liquid is delivered by a supply lineit to an injector I! by which it is introduced in a controlled mannerand in liquid phase into the oxygen stream in supply line it.

The water injector itself is shown in. greater detail in Fig. 2. Itcomprises a block 19 adapted to be connected in the oxygen supply line 11 and having a gas passage is extending length wise through it whichconstitutes, in effect, a portion of the oxygen supply line. A pipe 29places the gas passage !9 in communication with a pressure chamber abovethe diaphragm 2! of a diaphragm-controlled valve The valve 22 controlsthe flow of water from the supply line 16 to a nozzle 23 adapted toinject the water in finely divided or atomized form into the oxygen asit passes through the passage it. As long as oxygen is being supplied tothe burner there is suihcient pressure exerted on top of the diaphragm21 to open the valve 22. and admit water to the injector nozzle 29. Whenno oxygen is passing through the passage 59 the pressure above thediaphragm 21 is insunicient to hold the valve 22 open, so it closes andshuts off the supply of water to the injector nozzle 23. Thus, water isprevented from accumulating in the system when the gas burner is not inoperation.

Another form of water injector that can be substituted for that shown inFig. 2 is illustrated in Fig. 3. The oxygen on its way to the gas burnerflows through an aspirator 29 having an inlet nozzle 25 and an outletpassage 29 leading to the gas burner. The oxygen passing through thenozzle 25 draws water from a water supply tank El up through a pipe 29and aspirates it so that the water in finely divided form is carriedalong in the oxygen stream. A constant supply of water may be maintainedin the tank 2! in any well-known Way. Here again, when the burner is notin use and no oxygen is flowing to it, no water is introduced into theoxygen supply line.

Still other types or" liquid injectors may be employed, but it ispreferable in every case that the injector be capable of stopping thewater flow automatically when the gas flow is interrupted to prevent anaccumulation of the liquid in the system.

While in the above-described gas burner system the liquid injector isassociated with the oxygen supply line, it should be understood that itcan be associated with the acetylene supply line 25 if it is desired toinject the vaporizable liquid into the acetylene stream, or a liquidinjector may be associated with both gas supply lines if it is desiredto introduce the vaporizable liquid into both of the gas streams. In anycase, the vaporizable liquid is so injected into the gas supply thatwhen a backfire occurs there will be suspended in the gas a smallquantity of the vaporizable liquid in finely divided form so that itwill prevent ignition of the newly formed com bustible gas mixture bythe lingering hot products of combustion in the manner previouslydescribed. The vaporizable liquid may be injected into either or both ofthe gas streams at any point upstream of the mixing region. This may beupstream of the mixer itself or at the mixer, provided that in thelatter case the mixer is of such a type that the vaporizable liquid canbe injected into one or both of the gases before the gases have had anopportunity to mix.

As previously stated, the quantity of vaporizable liquid that must beinjected into one of the gases supplied to the gas burner to preventflashbacks is relatively small, especially when water which has a highlatent heat of vaporization constitutes the vaporizable liquid. Forexample, it has been found that in an oxyacetylene gas burner system onecubic centimeter of Water per cubic foot of acetylene burned gaveoptimum flashback resistance. The quantity of water required will ofcourse differ with different installations, but as a general rule it maybe stated that the amount of water required in an oxyacetylene gasburner system ranges from .25 to 5.0 cubic centimeters per cubic foot ofacetylene burned, although the invention, of course, is not limited eventothis water consumption range. This small quantity of water has noapparent effect on the functioning of the gas burner or the variousoperations performed by it such as welding and heat treatment of metal.

I claim:

1. in a gas burner system in which a fuel gas and acombustion-supporting gas are supplied separately to a mixing region andthe gas mixture is fed to a place at which it is burned, the method ofreducing the tendency of the mixed gases to continue burning after abackfire has occurred, which comprises continuously supplying anon-combustible vaporizable liquid in liquid phase to the mixing regionin at least one of said gases by continually injecting the liquid inliquid phase into said one of the gases while on its way to said placeof burning of the mixed gases in such quantity that the liquid ispresent at the mixing region in liquid phase.

2, A method according to claim 1 in which the ncn-combustiblevaporizable liquid is Water.

3. A me cod according to claim 1 in which the fuel gas is acetylene andthe combustion-supporting gas is oxygen.

4. A method according to claim 3 in which the non-combustiblevaporizable liquid is water.

5. A method according to claim 4 in which the amount of water introducedis at least 9.25 cu. cm. per cu. ft. of acetylene supplied.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,213,159 Dalen Jan. 23, 1917 1,423,155 Ruff July 18, 19221,519,830 Goeriz Dec. 16, 1924 1,588,983 Noval: June 15, 1926 ,033,910Russell Mar. 3, 1936 FOREIGN PATENTS Number Country Date 554,664 GermanyJuly 14, 1932 941,332 Germany Jan. 28, 1937 694,129 Germany July 25,1940

